1. Field of the Invention
The present invention relates to polyester-based artificial hairs, which can be heatset to curl or wave at low temperatures causing no sublimation or migration of disperse dyes and keeps well the shape thus heatset and to the process for producing the same.
2. Description of the Prior Art
Commercial artificial hairs used for wigs and toupees made principally of synthetic fibers have various drawbacks. For example, modacryl fiber and polyvinyl chloride fiber have low strength and hence readily break when combed after they have been waved. Furthermore, their most serious drawback is that the curl or wave of them will be lost under such conditions as ordinary bath, hot shower, sauna and sports in the sunshine, thereby clearly disclosing the fact that they are artificial hairs. In other words, they are poor in durability of the shapes once heatset, resulting in ready deformation of the shape under the above conditions.
Application of polyethylene terephthalate (hereinafter referred to as PET) has been attempted for improving the durability of the heatset shapes, with some success, and artificial hairs of PET are now commercially available to some extent.
PET fibers are in most cases dyed with disperse dyes, with some being dope-dyed though. Most of wigs and toupees utilizing artificial hair are used in the form of mixture of groups of multiplicity of filaments, which groups have different colors or color shades. Such mixture is wrapped several times around a steel pipe and heatset in an oven at 180 to 200.degree. C. for at least 10 minutes, or wrapped around a curing iron and then heatset. At this time, troubles often occur by the sublimation and migration of the disperse dyes on the filaments causing soiling or color change. This is caused by the fact that conventional PET fiber must be heatset at high temperatures. Against these troubles, the heatsetting may be conducted at a lower temperature with a prolonged setting time. Then, both the durability of heatset shape and prevention of migration of disperse dye can to some extent be achieved but with unavoidable increase in setting cost and shortage in the durability of the shapes heatset.
The heatset temprature of polyester fiber is decreased by copolymerization to decrease its melting point and/or glass transition temperature, which method is known to be applicable to conventional polyester fibers such as those for clothing use. Thus, polyester fibers are modified by such acid component as isophthalic acid, sodium 5-sulfoisophthalate, adipic acid, azelaic acid, malonic acid or succinic acid; or by such glycol component as butanediol, triethylene glycol, hexanediol, cyclohexanedimethanol, diethylene glycol, neopentyl glycol or nonanediol.
However, although in the polyesters modified by copolymerization of the above-mentioned component the melting point and/or glass transition temperature can be decreased to the desired level by controlling the copolymerization ratio so that they can be heatset more easily, it has been found that artificial hair filaments made from such polymers still have a drawback of readily destroying their once formed curls or waves by combing or brushing, in other words being inferior in the stability and durability of the heatset shapes. Such inferiority in the shape keeping performance after heatsetting may be attributed to the fact that both the above-mentioned acid components and glycol components have the function of increasing the number of bendings in the molecules of the polyesters.
Accordingly, an object of the present invention is to provide a polyester artificial hair which can readily be formed into curls or waves by using an iron or hot-air dryer and which assures excellent durability of the shapes thus formed over a long period of use.
Another object of the present invention is to provide a process for producing such an artificial hair.